Mold for continuous casting of metals, temperature measurement system and system and method for detecting breakthrough in a facility for continuous casting of metals

ABSTRACT

The invention relates to an ingot mold for continuous casting of metals, of the type consisting of an assembly of metal plates backed by cooling devices configured to allow the cooling of the metal plates by the circulation of a cooling fluid, comprising: a) at least one optical fiber, having a plurality of Bragg filters, extending in a wall of at least one of the plates, b) at least one groove formed in a wall of at least one of the plates, in a direction that is not parallel to the casting axis of the ingot mould in at least one portion of the length, the optical fiber extending in the groove, and c) a tongue of shape substantially complementary to the groove closing the groove over its entire length, the groove and the tongue having a shape suitable for the passage of the optical fiber.

The invention concerns a facility for continuous casting of metals. The invention more particularly concerns an ingot mold for continuous casting of metals. According to others of its aspects the invention concerns a system for measuring the temperature in a facility for continuous casting of metals as well as a system and a method for detection of breakout in a facility for continuous casting of metals.

A facility for continuous casting of metals, for example a facility for continuous casting of steel, generally includes an ingot mold into which a liquid metal is poured so that it will solidify in a suitable shape. This may for example be a bottomless ingot mold, in which case the metal cools to form a slab. In order to cool the liquid metal, walls of the ingot mold are alongside or backed by cooling devices, for example of the liquid-cooled type. The ingot mold and the cooling devices are sized according to the rate of flow of the metal so that the slab, when it leaves the ingot mold, has a solidified external surface of sufficiently great thickness to trap the metal that is still liquid located at the core of the slab.

During the pouring of the liquid metal into the ingot mold, it would be desirable to be able to have access in real time to measurements of the temperature at various points on the walls of the ingot mold. For example, it can happen that the metal adheres to the walls of the ingot mold, which is undesirable and can have considerable consequences for the productivity of the facility. This in particular generates the well-known phenomenon of breakout. The adhesion of the metal to the wall creates a zone in the slab in which the solidification of the metal does not occur appropriately, so that the slab leaves the ingot mold with an external surface of insufficient thickness in this zone. It follows that it tears and allows the metal still liquid at the core of the slab to flow out of the latter. Over and above the loss of efficiency, the liquid metal, which is therefore at a very high temperature, can damage the facility or even constitute a danger to operatives of the facility. It is therefore necessary to detect as soon as possible these breakouts in order to be able to take preventive measures, for example to slow down the rate of extraction of the slab, temporarily to shut down the facility or any other corrective measure.

There is known in the prior art a method for detecting if the metal is adhering to the walls of the ingot mold, a sign of an imminent breakout. It is based on measuring the temperature of the walls of the ingot mold at various points. In fact, it has been noted that the walls have a particular temperature profile when the metal adheres to them. A known means of measuring that temperature consists in installing regularly distributed thermocouples on the walls of the ingot molds so as to be able to detect any temperature anomaly as soon as possible.

This detection method is of interest but poses certain problems. In fact, to be able to measure the temperature of the walls at a maximum number of positions it is necessary to install a great number of thermocouples. This not only increases the cost of producing the ingot mold but also complicates the electrical connection of the thermocouples. Moreover, the thermocouples do not always enable precise and reliable measurement of the temperature of the walls, and so an unsatisfactory number of false alarms may be generated, that is to say alarms indicating an imminent breakout when this is not the case.

Another problem is linked to the configuration of the ingot mold, which usually consists of an assembly of metal plates backed by cooling devices configured to enable cooling of the metal plates by circulating a cooling fluid. To reach the zones of the ingot mold where the temperature must be measured it is necessary to pass through this cooling device and therefore through the circulating water. This leads to other problems of sealing and wiring.

Belgian patent application 2018/5193 already proposes a solution to this problem that consists in furnishing at least one of the walls of the ingot mold with a channel into which is inserted an optical fiber including a plurality of Bragg filters. This solution is noteworthy and furnishes an appropriate response to the problems mentioned above. Nevertheless, the inventors have sought to develop alternatives that could be implemented in a faster and less costly manner and could be adapted to suit complex ingot mold configurations.

An aim of the invention is to improve breakout detection by remedying the disadvantages set out hereinabove.

To this end there is provided in accordance with the invention an ingot mold for continuous casting of metals of the type consisting of an assembly of metal plates backed by cooling devices configured to allow cooling of the metal plates by the circulation of a cooling fluid, including:

-   -   at least one optical fiber including a plurality of Bragg         filters extending in a wall of at least one of said plates,     -   at least one groove formed in a wall of at least one of said         plates, in a direction that is not parallel to the casting axis         of the ingot mold in at least one portion of the length, the         optical fiber extending in the groove, and     -   a tongue of substantially complementary shape to the groove         closing the groove over its entire length, the groove and the         tongue having a shape suitable for the passage of the optical         fiber.

To avoid any confusion, it is here specified that the terminology of the dimensions of the plate is established as follows: the length and the width are the dimensions of the plate in a section perpendicular to the casting axis of the ingot mold and the depth is the dimension of the plate on the axis of the ingot mold.

Thus the thermocouples of the prior art are replaced by an optical fiber including Bragg filters. By means of the emission of a light beam in the fiber and the detection of the reflected and/or transmitted beam, the latter enable measurement of the temperature in the wall at the level of each of the filters. Clearly the groove, the optical fiber and the tongue are much less bulky than the thermocouples and clearly these items are much simpler to install. Moreover, temperature measurement using Bragg filters is more accurate than that obtained using thermocouples, which reduces the number of false alarms.

The tongue advantageously consists of a plurality of parts.

The length of the tongue can therefore be adapted by choosing the number of parts of which it consists. This enables adaptation to the dimensions of the ingot mold.

The tongue advantageously includes an attached part formed entirely before closing the groove.

The tongue is therefore entirely formed before its installation in the ingot mold. In other words, the tongue is not formed in situ at the moment of closing the groove. This facilitates its installation because it is possible to install the tongue in the ingot mold simply by depositing it in the groove or by causing it to slide along the groove from one of the ends of the groove. The groove advantageously has a substantially uniform depth.

The transfers of heat between the plates the optical fiber are therefore just as uniform.

The ingot mold is advantageously made of copper or of copper alloy, the tongue advantageously being made of the same material.

These materials have a high thermal conductivity and thus contribute to producing a uniform transfer of heat.

The tongue is preferably welded to the ingot mold in such a manner as to close the groove by electron beam welding, although other welding techniques are equally possible, such as for example laser welding, x-ray welding or ion welding and all types of arc welding, including electric arc welding with coated electrodes, arc welding with non-fusible electrodes, arc welding with fusible electrodes, submerged arc welding, electrogas welding, diffusion welding, or brazing or soldering.

Sealed closure of the groove is therefore made possible.

The groove is advantageously situated on at least one central part of at least one of the plates.

It is therefore possible to measure the temperature in a central zone of the wall and thus to obtain a measurement that is particularly representative of the temperature of the wall.

In accordance with one embodiment, the groove extends the entire length of at least one of the plates.

The temperature of the cast metal can therefore be measured at a great number of points, which contributes to reliable breakout detection.

The optical fiber is advantageously provided with a coating or with a tube.

Thus the optical fiber is protected from mechanical loads that could damage it. Moreover, the coating or the tube enables modulation of the diameter of the optical fiber.

The optical fiber advantageously has a diameter greater than 1.6 mm.

The ingot mold advantageously includes a plurality of optical fibers contained in a plurality of substantially parallel grooves.

The number of points for measuring the temperature of the wall is therefore further increased, which contributes to more reliable detection of breakout.

When the ingot mold is the type for casting a thin slab and includes a funnel portion in the upper part, the groove is advantageously located at least in all of the funnel part. In fact, the solution proposed in Belgian patent application 2018/5193 consisting in installing the optical fiber in a channel pierced in a manner substantially parallel to the wall is very difficult to put into practise in a non-plane portion of the wall.

It is clear that this embodiment is suitable for any type of ingot mold of complex shape.

The wall will advantageously include a groove in the funnel central part and a channel pierced in the plane part, the channel opening into the groove.

There is also provided in accordance with the invention a system for measuring the temperature in a system for continuous casting of metals, including:

-   -   an ingot mold as defined hereinabove,     -   an emitter-receiver adapted to send light in the optical fiber         and to receive the reflected and/or transmitted light received         by the emitter-receiver,     -   a processor adapted to transform data on the reflected and/or         transmitted light received by the emitter-receiver into         information on the temperature at various points on the ingot         mold, and     -   a terminal including a user interface, connected to the         processor.

There is also provided in accordance with the invention a system for detection of breakout in a system for continuous casting of metals, including a temperature measurement system as defined hereinabove in which the processor is adapted to transform data on the reflected and/or transmitted light received by the emitter-receiver into information on the detection of a breakout.

There is finally provided in accordance with the invention a method of detecting a breakout in a facility for continuous casting of metals, characterized in that the temperature is measured of a wall of an ingot mold as defined hereinabove.

An embodiment of the invention will now be described by way of nonlimiting example and with reference to the appended figures, in which:

FIG. 1 is a general view of a facility for continuous casting of metals including an ingot mold in accordance with the invention,

FIGS. 2a and 2b are schematics illustrating the functioning of the facility 5 from FIG. 1,

FIG. 3 is a view in section of the ingot mold of the facility from FIG. 1,

FIG. 4 is a perspective view of the ingot mold from FIG. 3,

FIG. 5 is a perspective view of a plate of the ingot mold from FIG. 3,

FIGS. 5a, 5b, 5c and 5d are schematics illustrating various shapes for a groove and for a tongue of the ingot mold,

FIG. 6 is a view in longitudinal section of an optical fiber contained in the plate from FIG. 5,

FIG. 7 is a schematic explaining the functioning of the optical fiber from FIG. 6, and

FIGS. 8a, 8b, 8c and 8d are views in section of the ingot mold from FIG. 3 illustrating the genesis of a breakout.

There has been represented in FIG. 1 a facility 2 for continuous casting of metals. It has a classic configuration, and so most of its components will be described only briefly.

The facility 2 includes ladles 4 containing liquid metal that it is wished to cool. Here there are two ladles 4 carried by a motorized arm 6. This motorized arm 6 is in particular able to move the ladles 4 that are brought full into the casting zone by a transport system (for example a traveling overhead crane, not represented) from a filling zone in which the molten metal may be poured into them, for example a furnace or a converter (not represented) before they are brought to the position illustrated in FIG. 1. After the ladle 4 is emptied, the motorized arm 6 also enables the empty ladle to be positioned in a position in which the transport system can take it up again and return it to the preparation zone where it will be reconditioned before returning to the filling zone.

The facility 2 includes a tundish or tundish basin 8 situated under the ladles 4. The latter have a bottom that can be opened enabling the liquid metal to flow into the tundish 8.

The tundish 8 includes a flow orifice that can be blocked by a stopper rod 10 that enables the flow of liquid metal to be controlled. The flow orifice of the tundish is extended by a submerged entrance (SEN) casting tube 11 for protection of the liquid metal poured into the ingot mold 12.

As is more visible in FIG. 2a and seen to a larger scale in FIG. 2b , the submerged entry casting tube 11 discharges into an upper opening of an ingot mold 12. Here this is a bottomless ingot mold having a casting axis that is vertical. The ingot mold 12 will be described in more detail later.

The facility 2 includes cooling devices 14 positioned on an external surface of the ingot mold 12. These are liquid type cooling devices. To this end they include pipes in which a refrigerant fluid, for example water, flows. The refrigerant fluid absorbs heat from the liquid metal located in the ingot mold 12 in order to cool it and to solidify it. Here the metal solidifies in the form of a slab having a solidified external surface 18 isolating a liquid core 20.

The facility 2 includes a roller guide 16 located downstream of the ingot mold 12. The guide 16 enables the slab, an external surface 18 of which has solidified, to be guided out of the ingot mold 12. As can be seen in FIG. 2a , the slab solidifies progressively as it moves in the guide 16. In other words, the greater the distance from the ingot mold 12 the greater the volume of the solidified external surface 18 of the slab and the smaller the volume of the liquid core 20 of the slab.

The ingot mold 12 is shown in more detail in FIG. 3. Here it features four plates 22 (the fourth not being visible because of the position of the section plane). The plates 22 are made of copper or of copper alloy, which are materials having high thermal conductivity and therefore facilitating exchanges of heat between the cooling devices 14 and the ingot mold 12. The plates 22 are arranged so that the ingot mold 12 has a globally rectangular or square cross section. The plates could however be arranged so that the ingot mold has a cross section of any other shape.

The ingot mold 12 has been represented from a different angle in FIG. 4. At least the upper part of the ingot mold 12 has a funnel shape 23 receiving part of the casting tube 11, the lower end of which is flattened. This shape is particularly suitable when the ingot mold is intended for casting thin slabs.

There has been represented in FIG. 5 one of the plates 22 of the ingot mold 12. It features a groove 24 extending in a direction that is not parallel to the casting axis. Here it extends in a substantially horizontal direction over the entire length of the plate. It is nevertheless possible for the groove 24 to extend over only a part of the length of the plate 22, for example the central part in the case of an ingot mold for casting thin slabs. The groove 24 has a substantially uniform depth over all its length.

There have been represented in FIGS. 5a to 5d various shapes that the groove 24 may take. The groove 24 is closed over all its length by a tongue 26 the shape of which is substantially complementary to that of the groove. The tongue 26 is preferably made of the same material as the plates 22, that is to say of copper or of copper alloy. The tongue 26 includes an attached part formed entirely before closing the groove 24. The tongue 26 is therefore entirely formed before its installation in the ingot mold 12. In other words, the tongue 26 is not formed in situ at the moment of closing the groove 24.

The groove 24 and the tongue 26 have a shape suitable for the passage of an optical fiber the function of which will be described below. In this instance, as can be seen in FIGS. 5a to 5d , the groove 24 or the tongue 26 (or both) has (or have) a slot 27 adapted to accommodate the optical fiber. Once the optical fiber is accommodated in the groove, the tongue 26 is welded on, for example by electron beam welding, in such a manner as to close the groove 24 over its entire length.

In a variant embodiment the tongue 26 consists of a plurality of parts welded together before the groove 24 is closed by the tongue 26. Thus the length of the tongue 26 can be modulated, in particular as a function of the length of the groove 24, by choosing the number of parts of which it consists.

In the embodiment from FIG. 5a the groove 24 and the tongue 26 have a curved profile and it is the tongue 26 that carries the slot 27.

In the FIG. 5b embodiment the groove 24 and the tongue 26 have a curved profile and it is the groove 24 that carries the slot 27.

In the FIG. 5c embodiment the groove 24 and the tongue 26 have a straight profile and it is the groove 24 that carries the slot 27.

In the FIG. 5d embodiment the groove 24 and the tongue 26 have a frustoconical straight section and it is the groove 24 that carries the slot 27. In particular, the section of the groove 24 is such that the groove widens in the direction of its depth. As a result, the shape of the groove 24 enables the tongue 26 to be held in position once placed in the groove 24, for example by causing it to slide along the groove 24 from one of its ends. It is therefore not necessary to weld the tongue 26 to the ingot mold 12, which represents an economic advantage. To enable easier insertion of the tongue 26 in the groove 24 it is possible to bend the plate very slightly about an axis parallel to the groove 24 situated on the other side of the plate 22, for example at the level of the groove. The groove 24 is therefore open and the tongue 26 can be slid into it without difficulty. This bending is preferably effected within the elastic deformation limit of the copper plate.

Referring to FIGS. 6 and 7, an optical fiber 28 is accommodated in the groove 24. The optical fiber 28 includes an optical sheath 30 as well as a core 32 surrounded by the optical sheath 30. The optical fiber 28 includes in its core 32 a plurality of Bragg filters 34. The optical fiber 28 includes at least ten Bragg filters per meter, preferably at least twenty Bragg filters per meter, more preferably at least thirty Bragg filters per meter, and even more preferably at least forty Bragg filters per meter.

The optical fiber 28 may equally be accommodated bare in the groove 24 or provided with a protective coating or inserted in a tube before being installed. This coating or tube may have the function of increasing the radius of the optical fiber 28 in order to fill all or almost all of the diameter of the groove 24. It is preferable for the optical fiber to have a diameter greater than 1.6 mm, given the possible presence of a coating or of a tube as mentioned hereinabove.

The functioning of the optical fiber 28 is illustrated in FIG. 7. The Bragg filters 34 are filters that enable reflection of light over a range of wavelengths centered on a predetermined value, termed the reflected wavelength, that can be adjusted by the manufacturer of the filter. This predetermined value is moreover a function in particular of the temperature of the filter, so that it is possible to write for each filter:

λ_(reflected) = f(λ₀, T)

where λ_(reflected) is the wavelength actually reflected by the filter, f is a known function, T is the temperature of the filter and λ₀ is the wavelength reflected by the filter at a predetermined temperature, for example at room temperature.

These two properties enable the optical fiber 28 to be used as a temperature sensor. Initially, there are installed in the optical fiber 28 Bragg filters 34 having distinct and chosen values of reflected wavelength λ₀, for example offset one by one by 5 nanometers. A light beam having a polychromatic spectrum 35 a, for example white light, is then sent in the optical fiber 28 after which the wavelength peaks represented in the spectrum of the reflected beam 35 b are determined. At each peak the measured value λ_(reflected) and the theoretical value of the reflected wavelength at ambient temperature λ₀ are compared and the temperature T of the filter in question is calculated using the function f. Alternatively, it is possible to effect these steps on the basis of gaps in the spectrum of the transmitted beam 35 c if the configuration of the channel 24 in which the optical fiber 28 is accommodated allows this.

Thus installation of the optical fiber 28 in one of the plates 22 of the ingot mold 12 makes it possible to measure the temperature of that plate at predetermined positions and to monitor its evolution over time. In order to obtain a sufficient number of measurement points it is preferable to place at least one optical fiber 28 in each of two facing plates 22, or even in each of the four plates 22 of the ingot mold 12.

Moreover, it is also preferable to place two optical fibers 28 in each plate 22 in such a manner as to be able to measure the temperature of the ingot mold 12 at two different heights. For example, the two optical fibers 28 may be placed in each plate so that they are parallel and spaced from one another by 15 to 25 centimeters.

Breakout detection is effected in the following manner.

There has been represented in FIGS. 8a to 8d the propagation of a zone 36 in which the metal contained in the ingot mold 12 adheres to one of the plates 22 of the latter. The graphs in the bottom right-hand zone of each of these figures represent the evolution of the temperature measured by a Bragg filter 34 of an upper optical fiber 28 a (upper curve) and by a Bragg filter 34 of a lower optical fiber (28 b) as a function of time.

As can be seen in the graphs in FIGS. 8a and 8b , the upper optical fiber 28 a detects an abnormal temperature increase that corresponds to adhesion of the metal to the ingot mold 12 in the zone 36. This is a first sign that a breakout is imminent.

Then, as can be seen in the graphs in FIGS. 8c and 8d , the lower optical fiber 28 b detects the abnormal temperature rise previously detected by the upper optical fiber 28 a. This is a second sign that a breakout is imminent, which serves as a confirmation that the breakout does not appear preventable.

In order for the information obtained by the optical fibers 28 a and 28 b to be communicated to the uses of the facility 2, the latter includes:

-   -   an emitter-receiver adapted to send light in the optical fiber         and to receive the reflected and/or transmitted light received         by the optical fiber,     -   a processor adapted to transform data on the reflected and/or         transmitted light received by the emitter-receiver into         information on the temperature at various points on the ingot         mold, and     -   a terminal including a user interface, connected to the         processor.

The processor is moreover adapted to transform the data on the reflected and/or transmitted light received by the emitter-receiver into information on the detection of a breakout.

Thanks to these elements (which have not been represented in the figures for reasons of clarity), it is possible to transform the temperature measurement effected by the optical fibers 28 into information understandable by the users of the facility 2 as to the detection or non-detection of a breakout. In other words, the ingot mold 12 equipped with the optical fibers 28, the emitter-receiver, the processor and the terminal form a breakout detection system. In the event of positive detection of a breakout, the users are able to take actions aimed at reducing the damage caused by the breakout or even to prevent it.

The invention is not limited to the embodiments presented and other embodiments will be clearly apparent to the person skilled in the art.

In particular the ingot mold may be more conventional with a straight shape with no funnel.

The ingot mold may be provided with a plurality of optical fibers contained in a plurality of substantially parallel grooves.

PARTS LIST

-   -   2: facility (for continuous casting of metals)     -   4: ladle     -   6: motorized arm     -   8: tundish     -   10: stopper rod     -   11: casting tube     -   12: ingot mold     -   14: cooling devices     -   16: guide     -   18: solidified external surface     -   20: liquid core     -   22: plate     -   23: funnel     -   24: groove     -   26: tongue     -   27: slot     -   28: optical fiber     -   30: optical sheath     -   32: core     -   34: Bragg filter     -   35 a: polychromatic spectrum     -   35 b: reflected beam spectrum     -   36: zone 

1. An ingot mold (12) for continuous casting of metals of the type consisting of an assembly (22) of metal plates backed by cooling devices (14) configured to allow cooling of the metal plates (22) by the circulation of a cooling fluid, the ingot mold having a casting axis and including: at least one optical fiber (28) including a plurality of Bragg filters (34) extending in a wall of at least one of said plates (22), at least one groove (24) formed in a wall of at least one of said plates (22), in a direction that is not parallel to the casting axis of the ingot mold (12) in at least one portion of the length, the optical fiber (28) extending in the groove (24), and a tongue (26) of substantially complementary shape to the groove (24) closing the groove over its entire length, the groove (24) and the tongue (26) having a shape suitable for the passage of the optical fiber.
 2. The ingot mold as claimed in claim 1, in which the tongue (26) consists of a plurality of parts.
 3. The ingot mold as claimed in claim 1, in which the tongue (26) includes an attached part formed entirely before closing the groove (24).
 4. The ingot mold as claimed in claim 1, in which the groove (24) has a substantially uniform depth.
 5. The ingot mold as claimed in claim 1, wherein the ingot mold is made of copper or copper alloy, the tongue (26) being made of the same material.
 6. The ingot mold as claimed in claim 1, in which the tongue (26) is welded, for example electron beam welded, to the ingot mold in such a manner as to close the groove (24).
 7. The ingot mold as claimed in claim 1, in which the groove (24) is situated on at least one central part of at least one of the plates (22).
 8. The ingot mold as claimed in claim 1, in which the groove (24) extends the entire length of at least one of the plates (22).
 9. The ingot mold as claimed in claim 1, in which the optical fiber (28) is provided with a coating or with a tube.
 10. The ingot mold as claimed in claim 1, in which the optical fiber (28) has a diameter greater than 1.6 mm.
 11. The ingot mold as claimed in claim 1, including a plurality of optical fibers (28) contained in a plurality of substantially parallel grooves (24).
 12. The ingot mold (12) as claimed in claim 1, of the type for pouring thin slabs, including a funnel portion (23) in the upper part, the groove (24) being located at least in the entire funnel part (23).
 13. A system for measuring the temperature in a system for continuous casting of metals, comprising: an ingot mold (12) as claimed in claim 1, an emitter-receiver adapted to send light in the optical fiber (28) and to receive the reflected and/or transmitted light received by the emitter-receiver as information on the temperature at various points on the ingot mold (12), a processor adapted to transform data on the reflected and/or transmitted light received by the emitter-receiver into information on the temperature at various points on the ingot mold, and a terminal including a user interface, connected to the processor.
 14. A system for detection of breakout in a system for continuous casting of metals, including a temperature measurement system as claimed in the preceding claim in which the processor is adapted to transform data on the reflected and/or transmitted light received by the emitter-receiver into information on the detection of a breakout.
 15. A method for detection of breakout in a facility for continuous casting of metals, characterized in that the temperature is measured of a wall of an ingot mold as claimed in claim
 14. 